Synthesis of iron-doped TiO2 nanoparticles by ball-milling process : the influence of process parameters on the structural, optical, magnetic, and photocatalytic properties

Titanium dioxide (TiO2) absorbs only a small fraction of incoming sunlight in the visible region thus limiting its photocatalytic efficiency and concomitant photocatalytic ability. The large-scale application of TiO2 nanoparticles has been limited due to the need of using an ultraviolet excitation source to achieve high photocatalytic activity. The inclusion of foreign chemical elements in the TiO2 lattice can tune its band gap resulting in an absorption edge red-shifted to lower energies enhancing the photocatalytic performance in the visible region of the electromagnetic spectrum. In this research work, TiO2 nanoparticles were doped with iron powder in a planetary ball-milling system using stainless steel balls. The correlation between milling rotation speeds with structural and morphologic characteristics, optical and magnetic properties, and photocatalytic abilities of bare and Fedoped TiO2 powders was studied and discussed.This work was partially financed by FCT-Fundacao para a Ciencia e Tecnologia-under the project PTDC/FIS/120412/2010: "Nanobased concepts for Innovative & Eco-sustainable constructive material's surfaces.

Structural and surface approach to the enhanced photocatalytic activity of sulfated TiO2 photocatalyst

TiO2 materials prepared by sol–gel method and then impregnated with sulfuric acid and further calcined at different temperatures show high photon efficiencies for the photocatalytic degradation of phenol under UV-illumination. Best photocatalyst was obtained after calcination around 700 8C, giving specific activities (i.e. per m2) significantly higher than those exhibited by similarly prepared non-sulfated TiO2 or by pure Degussa P25. Structural analysis of these new materials by XRD, TG–DTG and Raman spectroscopy shows that once calcined at 700 8C the material was a well-crystallized, high surface area and sulfate-free 90% anatase. Surface characterization in this work by XPS, LEIS and 1H MAS-NMR confirms a complete loss of the sulfate and OH-groups, and a low XPS O/Ti-atomic ratio with the O(1s) peak shifted to higher binding energies (1.7 versus 2 _ 0.1 and 530.4 eV versus 529.8 eV, respectively, against the reference materials). This indicates the existence of oxygen vacancies, which give a broad band at 400–600 nm in the reflectance spectra. However, LEIS spectra show an O/Ti composition at the topmost exposed atomic surface layer similar to that of TiO2 reference materials. Adsorption microcalorimetry of pyridine gives a profile of acid sites quite similar to those found for reference anatase samples, what discards the presence of superacid sites as the origin of its enhanced UV-photoefficiency. A mechanism is proposed, on the basis of earlier results in the literature for acidic TiO2 surfaces, to explain the nature of these materials. We also try to correlate the contribution of the oxygen vacancies within the anatase sub-surface layers to the high photon UV-efficiency of the system and, likely, to an enhanced vis-photoactivity of these materials